The electrical power requirements for electric vehicles (EV) or hybrid electric vehicles (HEV) can be very high. The battery will undergo discharging and charging cycles during vehicle start up/running mode and running/braking/internal and external charging mode respectively. The management of battery state of health, battery state of charge and battery temperature is critical in electric vehicle or hybrid electric vehicle applications when electric power cannot be interrupted during driving. And, different battery types, voltage and power requirements in different electric vehicles or hybrid electric vehicles may require different battery management systems. Therefore, the battery power supply system framework may be totally different from one vehicle design to another vehicle design due to the differences in battery type, power requirement and vehicle operating voltage. Sometimes the charging and replacement time of the battery packs may create a temporary interruption to user. A failed battery pack may cause the electric vehicle or hybrid electric vehicle to malfunction instantly. Conventionally, the battery packs (or cells) are connected in series forming a Battery Pack Assembly (BPA) in order to provide high voltage and high current to the electric vehicle or hybrid electric vehicle motors and other auxiliary systems. Since the battery packs or cells are connected in series, the charging and discharging current will flow through each battery pack (or cell) simultaneously. This causes problems in balancing individual battery pack (or cell) characteristics. A conventional battery management system detects the individual battery pack's (cell's) state of charge, state of health and battery temperature through complicated battery management design because of the serial connections between batteries. Individual battery pack (or cell), depending on the detected battery pack (or cell) condition, will be switched to be connected with (ON) or disconnected from (OFF) the serial connected battery packs (or cells). As a result, the BPA output voltage fluctuates. This will cause instability problem to motor drivers and associated circuits. Therefore, a DC/DC converter will be employed to convert the fluctuating BPA output voltage to a stable voltage supply for motor drivers and associated circuits. However, the DC/DC converter must operate at high voltage and high current conditions. The high power dissipation in the DC/DC converter generally lowers the reliability of the overall system. The system will shut down whenever the DC/DC converter fails. Further, the battery pack assembly (BPA) power cannot be easily increased or decreased to match with different loading requirements. Furthermore, a dead battery pack or cell cannot be replaced until the battery pack assembly (BPA) is disassembled from the vehicle.
Accordingly, there is a need in the art for an improved battery management system with fault tolerant features to resolve the battery imbalance and dead cell problems. Further, additional features such as variation of power bus voltage, power output capacity and number of batteries are desired to be achieved.
The above description of the background is provided to aid in understanding a fault tolerant modular battery management system, but is not admitted to describe or constitute pertinent prior art to the fault tolerant modular battery management system disclosed in the present application.